Adenocarcinoma, arising from the bronchial mucosal glands, is the most frequent non-small cell lung cancer in the United States, representing 35-40% of all lung cancers, and usually occurs in a peripheral location within the lung. Adenocarcinoma is the most common histologic subtype, and may manifest as a “scar carcinoma.” This is the subtype observed most commonly in persons who do not smoke and may manifest as multifocal tumors in a bronchoalveolar form.
Bronchoalveolar carcinoma is a distinct subtype of adenocarcinoma with a classic manifestation as an interstitial lung disease on chest radiograph. Bronchoalveolar carcinoma arises from type II pneumocytes and grows along alveolar septa. This subtype may manifest as a solitary peripheral nodule, multifocal disease, or a rapidly progressing pneumonic form. A characteristic finding in persons with advanced disease is voluminous watery sputum.
Squamous cell carcinoma accounts for 25-30% of all lung cancers. The classic manifestation is a cavitary lesion in a proximal bronchus. This type is characterized histologically by the presence of keratin pearls and can be detected based on results from cytologic studies because it has a tendency to exfoliate. It is the type most often associated with hypercalcemia.
Large cell carcinoma accounts for 10-15% of lung cancers, typically manifesting as a large peripheral mass on chest radiograph. Histologically, this type has sheets of highly atypical cells with focal necrosis, with no evidence of keratinization (typical of squamous cell carcinoma) or gland formation (typical of adenocarcinomas).